On-die termination circuit and driving method thereof

ABSTRACT

An on-die termination circuit is capable of increasing a resolution without enlargement of a chip or a layout size. The on-die termination circuit includes a control means, a termination resistance supply means, a code signal generating means. The control means sequentially generates a plurality of control signals in a response to a driving signal. The termination resistance supply means supplies a termination resistance in response to a coarse code signal having a plurality of bits and a fine code signal having a plurality of bits. The code signal generating means controls the fine code signal and the coarse code signal in response to the plurality of the control signals in order that the termination resistance has a level which is correspondent to an input resistance.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority of Korean patent application no.10-2006-0094052, filed in the Korean Patent Office on Sep. 27, 2006,which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor design technology; moreparticularly, to an on-die termination circuit capable of compensatingfor an error in resolution.

Generally, various semiconductor devices implemented by integratedcircuits such as CPU, memories and gate arrays are used for variousdigital products such as personal computers, servers and work stations.For the most part, the semiconductor devices have a receiving circuitfor receiving signals from external circuits through input pads and anoutput circuit for providing internal signals to the external circuitsthrough output pads.

Meanwhile, as the operation speed of the digital products becomeshigher, the swing of the signals which are interfaced between thesemiconductor devices is decreased. The reason why the swing is gettingsmaller is that it is necessary to minimize the transmission time of thesignals. However, the smaller the swing is, the more the semiconductordevices are influenced by external noise and the more the echo-backsignal caused by impedance mismatching is serious at the interface. Theimpedance mismatching is generated by an external noise, a change ofpower supply voltage or temperature and a change of manufacturingprocess of the semiconductor devices. If the impedance mismatching iscreated, it is difficult to transmit the data at high speed and the dataoutputted from an output terminal of the semiconductor device can bedistorted. Therefore, in the case that the semiconductor device at thereceiving side receives the distorted output signal through its inputterminal, the problems such as setup/hold failure or the misjudgment ofan input signal level can be caused frequently.

Therefore, the semiconductor device at the receiving side, in which thehigh speed operation is required, employs an impedance matching circuit,which is called on-die termination, in the vicinity of a pad within theintegrated circuit chip. Generally, as to the on-die termination scheme,a source termination is carried out at the transmitting side by theoutput circuit and a parallel termination is performed at the receivingside by a termination circuit which is in parallel coupled to areceiving circuit connected to the input pad.

FIG. 1 is a block diagram illustrating an on-die termination circuit ofa conventional semiconductor memory device.

Referring to FIG. 1, the on-die termination circuit according to theconventional semiconductor memory device includes: an ODT control unit30 for sequentially activating a plurality of control signalsODT_EN1P/N, ODT_EN2P/N and DT_UPP/N, in this order, in response to adriving signal RES; a first resistance feedback unit 20 to receive apull-up code signal P_LEG_CD<0:4> and an input resistance ZQ foroutputting a feedback pull-up resistance P_LEG_FD; a first terminationresistance supply unit 10 for outputting a pull-up resistance P_LEG_RSScorresponding to the pull-up code signal P_LEG_CD<0:4>; a first codesignal adjusting unit (including the reference numerals 40 and 50) foradjusting the pull-up code signal P_LEG_CD<0:4> in response to theplurality of control signals ODT_EN1P, ODT_EN2P and DT_UPP in order thatthe feedback pull-up resistance P_LEG_FD has a level corresponding to areference resistance RSS_REF; a second resistance feedback unit 70 toreceive a pull-down code signal N_LEG_CD<0:4> and the pull-up codesignal P_LEG_CD<0:4> for outputting a feedback pull-down resistanceN_LEG_FD; a second code signal adjusting unit (including the referencenumerals 80 and 90) for adjusting the pull-down code signalN_LEG_CD<0:4> in response to a plurality of control signals ODT_EN1N,ODT_EN2N, DT_UPN in order that the feedback pull-down resistanceN_LEG_FD has a level corresponding to the reference resistance RSS_REF;and a second termination resistance supply unit 60 for outputting apull-down resistance N_LEG_RSS corresponding to the pull-down codesignal N_LEG_CD<0:4>.

Here, the first code signal adjusting unit includes: a first leveldetecting unit 42 for detecting a level of the feedback pull-upresistance P_LEG_FD, based on the reference resistance RSS_REF, inresponse to the control signal ODT_EN1P and for outputting a pull-updetecting signal P_LEG_SN; a first amplifier 44 for amplifying thepull-up detecting signal P_LEG_SN in response to the control signalODT_EN2P and for outputting a pull-up level signal P_LEG_DT; and a firstregister 50 for storing the pull-up level signal P_LEG_DT and outputtingthe pull-up code signal P_LEG_CD<0:4> in response to the control signalDT_UPP.

Similarly, the second code signal adjusting unit includes: a secondlevel detecting unit 82 for detecting a level of the feedback pull-downresistance N_LEG_FD, based on the reference resistance RSS_REF, inresponse to the control signal ODT_EN1N and for outputting a pull-downdetecting signal N_LEG_SN; a second amplifier 84 for amplifying thepull-down detecting signal N_LEG_SN in response to the control signalODT_EN2N and for outputting a pull-down level signal P_LEG_DT; and asecond register 90 for storing the pull-down level signal P_LEG_DT andoutputting the pull-down code signal N_LEG_CD<0:4> in response to thecontrol signal DT_UPN.

At the time of the activation of the driving signal RES, the ODT controlunit 30 sequentially activates the control signals ODT_EN1P, ODT_EN2Pand DT_UPP and then the control signals ODT_EN1N, ODT_EN2N and DT_UPN.Thereafter, this operation is repeated for a predetermined number oftimes under the control of the ODT control unit 30.

Even though it is not shown in FIG. 1, the pull-up resistance P_LEG_RSSand the pull-down resistance N_LEG_RSS are on-die terminationresistances which are coupled to the corresponding data pads.

Also, the first level detecting unit 42 includes a current mirror typedifferential amplifier to which the feedback pull-up resistance P_LEG_FDand the reference resistance RSS_REF are applied and the second leveldetecting unit 82 also includes a current mirror type differentialamplifier. The first and second amplifiers 44 and 84 respectivelyinclude a voltage cross-coupled amplifier. The first and secondregisters 50 and 90 respectively include a latch to latch thecorresponding input signals P_LEG_DT and N_LEG_DT in response to thecorresponding control signals DT_UPP/N.

FIG. 2 is a schematic circuit diagram illustrating the first resistancefeedback unit 20 described in FIG. 1. Referring to FIG. 2, the firstresistance feedback unit 20 includes first to fifth PMOS transistors,which are turned on in response to the corresponding pull-up code signalP_LEG_CD<0:4>, and first to fifth resistors each of which is connectedbetween a common output node and a respective PMOS transistor. Thefeedback pull-up resistance P_LEG_FD is a signal corresponding to thelevel of voltage applied to the common output node.

The first resistance feedback unit 20 receives the input resistance ZQat its output node and the input resistance ZQ is applied from anexternal circuit through an input pin. The resistance of 240Ω is appliedbetween the input pin and a ground voltage. Therefore, in the firstresistance feedback unit 20, the number of transistors, which are turnedon, is determined by the pull-up code signal P_LEG_CD<0:4>. The feedbackpull-up resistance P_LEG_FD is determined by parallel resistance valueof resistors which are in series connected to their respective turn-onPMOS transistors.

On the other hand, the first termination resistance supply unit 10,which has the same configuration as the first resistance feedback unit20 shown in FIG. 2, supplies the pull-up resistance P_LEG_RSS.

FIG. 3 is a schematic circuit diagram illustrating the second resistancefeedback unit 70 described in FIG. 1.

As shown in FIG. 3, the second resistance feedback unit 70 includes afirst resistance unit 32, which is connected to an output node, in orderto supply a first code resistance corresponding to the pull-up codesignal P_LEG_CD<0:4> and a second resistance unit 34, which is connectedto the output node, in order to supply a second code resistancecorresponding to the pull-down code signal N_LEG_CD<0:4>. The feedbackpull-down resistance N_LEG_FD is a signal corresponding to the level ofvoltage applied to the output node.

The first resistance unit 32 includes first to fifth PMOS transistors,which are turned on in response to the corresponding pull-up code signalP_LEG_CD<0:4>, and first to fifth resistors each of which is connectedbetween a common output node and each PMOS transistor. The secondresistance unit 34 includes first to fifth resistors, each of which isconnected to the common output node, and first to fifth NMOStransistors, which are disposed between the resistors and the groundvoltage VSSQ and respectively turned on in response to the correspondingpull-down code signal N_LEG_CD<0:4>.

That is, the second resistance feedback unit 70 supplies the feedbackpull-down resistance N_LEG_FD which is determined by a ratio of thefirst and second code resistance, by disposing in series both the firstcode resistance corresponding to the pull-up code signal P_LEG_CD<0:4>and the second code resistance corresponding to the pull-down codesignal N_LEG_CD<0:4> at its output node. The second terminationresistance supply unit 60, which has the same configuration as thesecond resistance unit 34 shown in FIG. 3, supplies the pull-downresistance N_LEG_RSS in response to the pull-down code signalN_LEG_CD<0:4>.

The operation of the on-die termination circuit shown in FIGS. 1 to 3will be described briefly.

First, the first resistance feedback unit 20, to which the pull-up codesignal P_LEG_CD<0:4> and the input resistance ZQ are applied, outputsthe feedback pull-up resistance P_LEG_FD. The ODT control unit 30sequentially activates the control signals ODT_EN1P, ODT_EN2P, DT_UPP inresponse to the activation of the driving signal RES. Next, the firstlevel detecting unit 42 outputs a pull-up detecting signal P_LEG_SN byamplifying a difference between the reference resistance RSS_REF and thefeedback pull-up resistance P_LEG_FD in response to the control signalODT_EN1P.

The first amplifier 44 outputs the pull-up level signal P_LEG_DT byamplifying the pull-up detecting signal P_LEG_SN in response to thecontrol signal ODT_EN2P. The first register 50 stores the pull-up levelsignal P_LEG_DT and outputs the pull-up code signal P_LEG_CD<0:4> inresponse to the control signal DT_UPP.

Also, the ODT control unit 30 sequentially activates the control signalsODT_EN1N, ODT_EN2N and DT_UPN. The second resistance feedback unit 70 towhich the pull-down code signal N_LEG_CD<0:4> and the pull-up codesignal P_LEG_CD<0:4> are applied outputs the feedback pull-downresistance N_LEG_FD corresponding to the pull-down resistance N_LEG_RSS.The second level detecting unit 82 outputs the pull-down detectingsignal N_LEG_SN by amplifying a difference between the referenceresistance and the feedback pull-down resistance N_LEG_FD in response tothe control signal ODT_EN1N.

Next, the second amplifier 84 outputs the pull-down level signalN_LEG_DT by amplifying the pull-down detecting signal N_LEG_SN inresponse to the control signal ODT_EN2N. The second register 90 storesthe pull-down level signal N_LEG_DT and outputs the pull-down codesignal N_LEG_CD<0:4> in response to the control signal DT_UPN.

The ODT control unit 30 repeatedly activates the control signalsODT_EN1P, ODT_EN2P, DT_UPP/ODT_EN1N, ODT_EN2N and DT_UPN in order thatthe above-mentioned processes are executed repeatedly for thepredetermined number of times. Therefore, if the pull-up codes signalP_LEG_CD<0:4> and the pull-down codes signal N_LEG_CD<0:4> are setthrough the above-mentioned processing, the first and second terminationresistance supply units 10 and 60 output the pull-up resistanceP_LEG_RSS and the pull-down resistance N_LEG_RSS corresponding to theinput resistance ZQ.

The conventional on-die termination circuit mentioned above producesboth the pull-up codes signal P_LEG_CD<0:4> and the pull-down codessignal N_LEG_CD<0:4> of 5 bits and provides the pull-up resistanceP_LEG_RSS and the pull-down resistance N_LEG_RSS through the codessignal. The pull-up codes signal P_LEG_CD<0:4> and the pull-down odessignal N_LEG_CD<0:4> is set in order that the pull-up resistanceP_LEG_RSS and the pull-down resistance N_LEG_RSS respectively have avalue of the input resistance ZQ.

The values of the pull-up and pull-down resistance are regulated by theactivation of the corresponding code of the 5 bits of codes signal. Thatis, according to the number of bits of the code signal, the resolutionof the pull-up and pull-down resistance is changed. For example, sincean increase in the number of bits of the code signal means the number oftransistors and resistors which are serially connected to them isincreased, the fluctuation of the pull-up and pull-down resistance isreduced. On the contrary, if the number of bits of the code signal isdecreased, the fluctuation of the pull-up and pull-down resistance isincreased.

Accordingly, if the number of bits of the code signal is increased andthe number of resistors and transistors controlled by the code signal isincreased, it is possible to obtain the high resolution. However, thereis a problem in that the size of a chip and layout is enlarged due tothe increment of the resistors and the MOS transistors. Moreover, theburden on the size of a chip and layout can be reduced when the numberof code signals is reduced; however, the resolution is decreased and alarge error may occur in the pull-up and pull-down resistance ascompared with the input resistance so that a malfunction is causedduring high frequency operation.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to provide an on-dietermination circuit capable of increasing a resolution withoutenlargement of a chip or a layout size.

In accordance with an aspect of the present invention, an on-dietermination circuit includes a control means for sequentially generatinga plurality of control signals in response to a driving signal, atermination resistance supply means for supplying a terminationresistance in response to a coarse code signal having a plurality ofbits and a fine code signal having a plurality of bits, and a codesignal generating means for controlling the fine code signal and thecoarse code signal in response to the plurality of the control signalsso that the termination resistance has a level which corresponds to aninput resistance.

In accordance with another aspect of the present invention, an on-dietermination circuit includes a driving control means for sequentiallygenerating a plurality of control signals in response to a drivingsignal, a first termination resistance supply means for supplying atermination pull-up resistance in response to a first coarse code signalhaving a plurality of bits and a first fine code signal having aplurality of bits, a first code signal generating means for controllingthe first coarse and fine code signals in response to the plurality ofthe control signals so that the termination pull-up resistance has alevel which corresponds to an input resistance, a second terminationresistance supply means for supplying a termination pull-down resistancein response to a second coarse code signal having a plurality of bitsand a second fine code signal having a plurality of bits, and a secondcode signal generating means for controlling the second coarse and finecode signals in response to the plurality of control signals so that thetermination pull-down resistance has a level which corresponds to thetermination pull-up resistance.

In accordance with a further aspect of the present invention, an on-dietermination circuit includes at least one passive resistance group,which has a plurality of units each having a MOS transistor and aresistor, for controlling resistance coarsely in response to a firstcode signal, wherein in each unit resistance, the resistor is in seriesconnected to the MOS transistor, and at least one active resistancegroup, which has a plurality MOS transistors, for controlling resistancefinely by selectively turning on the plurality of MOS transistors inresponse to a second code signal, wherein the passive resistance groupis in series connected to the active resistance group and the MOStransistors in the active resistance group are in parallel connected toeach other.

In accordance with a further aspect of the present invention, an on-dietermination circuit includes a termination resistance supply unit forsupplying a termination resistance in response to a coarse code signalhaving a plurality of bits and a fine code signal having a plurality ofbits, a resistance feedback unit for receiving the fine code signals andthe coarse code signals and for outputting a feedback pull-downresistance, a coarse code generating unit for producing the coarse codesignal in order that the feedback pull-down resistance has a levelcorresponding to a reference resistance, and a fine code generating unitfor producing the fine code signal in order that the feedback pull-downresistance has a level corresponding to the reference resistance whilethe coarse code signal generating unit is inactivated.

In accordance with a further aspect of the present invention, a methodfor driving an on-die termination circuit includes controlling a coarsecode signal of a plurality of bits to supply a termination resistancecorresponding to an input resistance, and controlling a fine code signalof a plurality of bits to supply the termination resistancecorresponding to the input resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an on-die termination circuit ofa conventional semiconductor memory device.

FIG. 2 is a schematic circuit diagram illustrating a first resistancefeedback unit described in FIG. 1.

FIG. 3 is a schematic circuit diagram illustrating a second resistancefeedback unit described in FIG. 1.

FIG. 4 is a block diagram illustrating an on-die termination circuit inaccordance with an embodiment of the present invention.

FIG. 5 is a schematic circuit diagram illustrating a first resistancefeedback unit described in FIG. 4.

FIG. 6 is a schematic circuit diagram illustrating a second resistancefeedback unit described in FIG. 4.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, a semiconductor memory device in accordance with thepresent invention will be described in detail referring to theaccompanying drawings.

FIG. 4 is a block diagram illustrating an on-die termination circuit inaccordance with an embodiment of the present invention. Referring toFIG. 4, the on-die termination circuit according to the presentinvention includes: an ODT control unit 800 for activating a pluralityof control signals ODT_EN1P/N, ODT_EN2P/N and DT_UPP/N in response to adriving signal RES; a first termination resistance supply unit 500 forsupplying a pull-up resistance P_LEG_RSS corresponding to a first coarsecode signal P_CR_CD<0:3> and a first fine code signal P_FN_CD<0:4>; afirst code signal generating unit for producing the first fine codesignal P_FN_CD<0:4> and the first coarse code signal P_CR_CD<0:3> inorder that the pull-up resistance P_LEG_RSS has a level which iscorrespondent to an input resistance ZQ; a second termination resistancesupply unit 700 for supplying a pull-down resistance N_LEG_RSScorresponding to a second coarse code signal P_CR_CD<0:3> and a secondfine code signal P_FN_CD<0:4>; and a second code signal generating unitfor adjusting the second fine code signal P_FN_CD<0:4> and the secondcoarse code signal P_CR_CD<0:3> in order that the pull-down resistanceN_LEG_RSS has a level which is correspondent to the pull-up resistanceP_LEG_RSS.

The first and second termination resistance supply units 500 and 700supplies the pull-up resistance P_LEG_RSS or the pull-down resistanceN_LEG_RSS by serially connecting first resistors and second resistors.The connection of the first resistors is also controlled by thecorresponding first and second coarse code signals P_CR_CD<0:3> andN_CR_CD<0:3>. The connection of the second resistors is also controlledby the corresponding first and second fine code signals P_FN_CD<0:4> andN_FN_CD<0:4>. The resistance fluctuation of the first resistorsaccording to the first and second coarse code signals P_CR_CD<0:3> andN_CR_CD<0:3> is larger than that of the second resistors according tothe first and second fine code signal P_FN_CD<0:4> and N_FN_CD<0:4>.Accordingly, the variation of the pull-up or pull-down resistance can bechanged by controlling the variation of the coarse and fine codesignals.

Meanwhile, the first code signal generating unit includes: a first codesignal generation control unit 100 for generating a pull-up level signalP_LEG_DT in response to the corresponding control signal, wherein thepull-up level signal P_LEG_DT corresponds to a level difference of thefirst fine code signal P_FN_CD<0:4> and the first coarse code signalP_CR_CD<0:3> based on the input resistance ZQ; a first control unit 320for controlling a first fine code register 340 and a first coarse coderegister 360; a first coarse code register 360 for outputting the firstcoarse code signal P_CR_CD<0:3> corresponding to the pull-up levelsignal P_LEG_DT at the time of an activation of the correspondingcontrol signal; and a first fine code register 340 for outing the firstfine code signal P_FN_CD<0:4> corresponding to the pull-up level signalP_LEG_DT at the time of a inactivation of the first coarse coderegister.

The first code signal generation control unit 100 includes: a firstresistance feedback unit 120, to which the input resistance ZQ, thefirst fine code signal P_FN_CD<0:4> and the first coarse code signalP_CR_CD<0:3> are applied, for outputting a feedback pull-up resistanceP_LEG_FD; a first level detecting unit 140 for outputting a pull-updetecting signal P_LEG_SN in response to the control signal ODT_EN1P bydetecting a level of the feedback pull-up resistance P_LEG_FD based on areference resistance RSS_REF; and a first amplifier 160 for amplifyingthe pull-up detecting signal P_LEG_SN in response to the control signalODT_EN2P and for-outputting the amplified signal as the pull-up levelsignal P_LEG_DT.

The first control unit 320 generates a first pull-up driving signalODT_UPP1 and a second pull-up driving signal ODT_UPP2 in response to thecontrol signal ODT_EN1P and the pull-up level signal P_LEG_DT. The firstfine code register 340 outputs the first fine code signal P_FN_CD<0:4>corresponding to the pull-up level signal P_LEG_DT in response to thecontrol signal DT_UPP and the first pull-up driving signal ODT_UPP1. Thefirst coarse code register 360 outputs the first coarse code signalP_CR_CD<0:3> corresponding to the pull-up level signal P_LEG_DT inresponse to the control signal DT_UPP and the second pull-up drivingsignal ODT_UPP2.

The first control unit 320 activates the second pull-up driving signalODT_UPP2 in response to the control signal ODT_EN1P. Thereafter, thefirst control unit 320 inactivates the second pull-up driving signalODT_UPP2 and activates the first pull-up driving signal ODT_UPP1 whenthe pull-up level signal P_LEG_DT goes from a high level to a low level.In other words, at the initial driving time of the on-die terminationcircuit in which the control signal ODT_EN1P is activated, the firstcontrol unit 320 activates the second pull-up driving signal ODT_UPP2 sothat the first coarse code register 360 is activated and then the coarsecode signal having a large variation range is calculated. When theresistance value has a level corresponding to the input resistance ZQaccording to the first coarse code signal P_CR_CD<0:3>, the voltagelevel of the pull-up level signal P_LEG_DT is changed and the fine codesignal P_FN_CD<0:4> is calculated based on the activation of the firstpull-up driving signal ODT_UPP1 in the first control unit 320.Therefore, the first control unit 320 makes the resistance valuecorresponding to the input resistance ZQ controlled in the largevariation range using the first coarse code signal P_CR_CD<0:3> andthereafter performs the fine adjustment through the first fine codesignal P_FN_CD<0:4>.

On the other hand, the second code signal generating unit includes: asecond code signal generation control unit 200 for outputting, inresponse to the corresponding control signal, a pull-down level signalN_LEG_DT, which corresponds to a level difference between the secondfine and coarse code signals N_FN_CD<0:4> and N_CR_CD<0:3> and the firstfine and coarse code signals P_FN_CD<0:4> and P_CR_CD<0:3>; a secondcontrol unit 420 for controlling a second fine code register 440 and asecond coarse code register 460; a second coarse code register 460 foroutputting the second coarse code signal N_CR_CD<0:3> corresponding tothe pull-down level signal N_LEG_DT in response to the correspondingcontrol signal; and a second fine code register 440 for outputting thesecond fine code signal N_FN_CD<0:4> corresponding to the pull-downlevel signal N_LEG_DT at the time of a inactivation of the second coarsecode register 460.

The second code signal generation control unit 200 includes: a secondresistance feedback unit 220, to which the first and second fine codesignals P_FN_CD<0:4> and N_FN_CD<0:4> and the first and second coarsecode signals P_CR_CD<0:3> and N_CR_CD<0:3> are applied, for outputting afeedback pull-down resistance N_LEG_FD; a second level detecting unit240 for outputting a pull-down detecting signal N_LEG_SN in response tothe control signal ODT_EN1N by detecting a level of the feedbackpull-down resistance N_LEG_FD based on the reference resistance RSS_REF;and a second amplifier 260 for amplifying the pull-down detecting signalN_LEG_SN in response to the control signal ODT_EN2N and for outputtingthe amplified signal as the pull-down level signal N_LEG_DT.

Meanwhile, the second control unit is the same as the first controlunit, except for the input signals, and the second coarse and fine coderegisters also are the same as the first coarse and fine code registers.Accordingly, they will be described briefly.

The second control unit 420 generates a first pull-down driving signalODT_UPN1 and a second pull-down driving signal ODT_UPN2 in response tothe control signal ODT_EN1N and the pull-down level signal N_LEG_DT. Thefirst fine code register 440 outputs the second fine code signalN_FN_CD<0:4> corresponding to the pull-down level signal N_LEG_DT inresponse to the control signal DT_UPN and the first pull-down drivingsignal ODT_UPN1. The second coarse code register 460 outputs the secondcoarse code signal N_CR_CD<0:4> corresponding to the pull-down levelsignal N_LEG_DT in response to the control signal DT_UPP and the secondpull-down driving signal ODT_UPN2.

The second control unit 420 activates the second pull-down drivingsignal ODT_UPN2 in response to the control signal ODT_EN1N. Thereafter,the second control unit 420 inactivates the second pull-down drivingsignal ODT_UPN2 and activates the first pull-down driving signalODT_UPN1 when the pull-down level signal N_LEG_DT goes from a high levelto a low level. In other words, the second control unit 420 drives thesecond coarse code register 460 at the initial driving time and drivesthe second fine code register 440 after the transition of the pull-downlevel signal.

The first level detecting unit 140 includes a current mirror typedifferential amplifier to which the feedback pull-up resistance P_LEG_FDand the reference resistance RSS_REF are applied and the second leveldetecting unit 240 also includes such a current mirror type differentialamplifier. The first and second amplifiers 160 and 260 include a voltagecross-coupled amplifier, respectively. Each of the first and secondfines code registers 340 and 440 and the first and second coarse coderegisters 360 and 460 can include a latch for latching correspondinginput signals P/N_LEG_DT at the time of activation of the correspondingcontrol signals DT_UPP/N and the driving signals.

The code signal generating unit can be classifies into a coarse codesignal generating unit to generate the coarse code signals P_CR_CD<0:3>and N_CR_CD<0:3> using the code signal generation control units (100 and200), control units (320 and 340) and the coarse code register units(360 and 460) and a fine code signal generating unit to generate thefine code signals P_FN_CD<0:4> and N_FN_CD<0:4> using the code signalgeneration control units (100 and 200), control units (320 and 340) andthe fine code register units (340 and 440).

The first and second resistance feedback units 120 and 220 respectivelyincludes a resistance unit of which the resistance value differentlyranges in response to each of the coarse code signals N_CR_CD<0:3> andP_CR_CD<0:3> and the fine code signals N_FN_CD<0:4> and P_FN_CD<0:4>.Accordingly, the variation of the feedback signal by the coarse and finecode signals is different. Also, even though it is not shown in FIG. 4,the pull-up resistance and the pull-down resistance are the on-dietermination resistances which are connected to the corresponding datapads.

As described above, the on-die termination circuit according to thepresent invention may support the high resolution, without increasing anarea of the device, and guarantee stable operation in the highfrequency, by making the internal resistance of the first and secondtermination resistance supply units 500 and 700 and the first and secondresistance feedback units 120 and 200 have a variety of fluctuationaccording to the corresponding input signals P_CR_CD<0:3>, N_CR_CD<0:3>,N_FN_CD<0:4> and P_FN_CD<0:4>. The present invention produces the firstfine code signal P_FN_CD<0:4> and the first coarse code signalP_CR_CD<0:3>, instead of the pull-up code signal P_LEG_CD<0:4>, and thesecond fine code signal N_FN_CD<0:4> and the second coarse code signalN_CR_CD<0:3>, instead of the pull-down code signal N_LEG_CD<0:4>, inorder to control a plurality of divided resistors individually. Thecoarse code signals P_CR_CD<0:3> and N_CR_CD<0:3> controls the feedbackresistance P_LEG_FD and N_LEG_FD and the termination resistanceP_LEG_RSS and N_LEG_RSS with a large width and sets up them to theresistance value corresponding to the input resistance ZQ at a highspeed. Thereafter, the fine adjustment to the input resistance ZQ iscarried out by the fine code signals P_FN_CD<0:4> and N_FN_CD<0:4>

The resistance adjustment will be described in detail referring to aschematic circuit of the resistance feedback unit. FIG. 5 is a schematiccircuit diagram illustrating the first resistance feedback unit 120described in FIG. 4. Referring to FIG. 5, the first resistance feedbackunit 120 includes a first pull-up resistance unit 122 for providing afirst pull-up code resistance corresponding to the first coarse codesignal P_CR_CD<0:3>, and a second pull-up resistance unit 124 forproviding a second pull-up code resistance corresponding to the firstfine code signal P_FN_CD<0:4>. The first and second pull-up resistanceunits 122 and 124 are serially connected between the power supplyvoltage VDDQ and an output node and a voltage applied to the output nodeis outputted as the feedback pull-up resistance P_LEG_FD.

The first pull-up resistance unit 122 includes a plurality of resistanceunits 122 a, 122 b, 122 c and 122 d which are connected to a first nodeN1 in response to the corresponding first coarse code signalP_CR_CD<0:3>, respectively. Since the plurality of resistance units 122a, 122 b, 122 c and 122 d have the same structure, only one resistanceunit will be described.

The resistance unit 122 a includes a first PMOS transistor PM1 having agate to receive the first coarse code P_CR_CD<0> and a source connectedto the power supply voltage VDDQ, and a first resistor Rp1 which isconnected between a drain of the first PMOS transistor PM1 and the firstnode N1.

In the second pull-up resistance unit 124, fifth to ninth PMOStransistors PM5 to PM9 which are respectively turned on by the fine codesignal P_FN_CD<0:4> are in parallel connected between the first node N1and the output node. For example, each of the first to fourth resistorsin the first pull-up resistance unit 122 has one of resistance values,240Ω, 120Ω and 60Ω. Also, the input resistance ZQ may be applied to theoutput node of the first resistance feedback unit 120. The inputresistance ZQ is an external signal applied through the input pin whichis connected to the ground voltage level through a resistance value of240Ω. Further, the first termination resistance supply unit 500, whichhas the same configuration as the first resistance feedback unit 120described in FIG. 5, provides the pull-up resistance P_LEG_RSS.Accordingly, the pull-up resistance P_LEG_RSS with the fine adjustmentis provided by the fine code signal P_FN_CD<0:4>.

In the first resistance feedback unit 120, the first pull-up coderesistance corresponding to the first coarse code signal P_CR_CD<0:3> isserially connected to the second pull-up code resistance correspondingto the first fine code signal P_FN_CD<0:4> between the power supply VDDQand the output node and the feedback pull-up resistance P_LEG_FD isoutputted by this serial connection of the two resistances.

More concretely, when the PMOS transistors PM1, PM2, PM3 and PM4 in theresistance units 122 a, 122 b, 122 c and 122 d are respectively turnedon by the activation of the corresponding coarse code signalP_CR_CD<0:3> in the first pull-up resistance unit 122, the resistorsRp1, Rp2, Rp3 and Rp4 are connected to the first node N1 respectively sothat the first pull-up code resistance is determined. In the secondpull-up resistance unit 124, the PMOS transistors PM5, PM6, PM7, PM8 andPM9, which are respectively turned on by the corresponding fine codesignal P_FN_CD<0:4>, are connected between to the first node N1 and theoutput node so that the second pull-up code resistance is determined.

The first pull-up resistance unit 122 controls the first pull-up coderesistance using the passive elements of the resistors Rp1, Rp2, Rp3 andRp4 of which resistance is larger than that of the PMOS transistors.Meanwhile, the second pull-up code resistance of the second pull-upresistance unit 124 is determined by the turn-on resistance of the PMOStransistors. Accordingly, the first pull-up resistance unit 122 cancontrol the first pull-up code resistance in a relatively large range byusing the passive elements of the resistors Rp1, Rp2, Rp3 and Rp4 andthe second pull-up resistance unit 124 can control the second pull-upcode resistance in a relatively small range by using the turn-onresistance of the PMOS transistors.

Therefore, being different from the conventional semiconductor device,the first resistance feedback unit 120 according to the presentinvention finely controls the feedback pull-up resistance P_LEG_FD byfurther including the second pull-up resistance unit 124 of the PMOStransistors and makes it possible to supply the termination resistancewith high resolution. Also, since the second pull-up resistance unit 124is included, the burden on the area is reduced. Particularly, eventhough it is possible to improve the resolution by increasing the numberof unit resistors in the first pull-up resistance unit 122, this maycause the increasing of the burden on the area because the area requiredin the passive resistors is larger than that in the transistors.

FIG. 6 is a schematic circuit diagram illustrating the second resistancefeedback unit 220 described in FIG. 4. Referring to FIG. 6, the secondresistance feedback unit 220 includes: a third pull-up resistance unit222 for supplying a first pull-up code resistance corresponding to thefirst fine code signal P_FN_CD<0:4>; a fourth pull-up resistance unit224 for supplying a second pull-up code resistance corresponding to thefirst coarse code signal (P_CR_CD<0:3>; a first pull-down resistanceunit 226 for supplying a first pull-down code resistance correspondingthe second fine code signal N_FN_CD<0:4>; and a second pull-downresistance unit 228 to supplying a second pull-down code resistancecorresponding the second coarse code signal N_CR_CD<0:3>. The third andfourth pull-up resistance units 222 and 224 are in series connected toeach other between the power supply voltage VDDQ and an output node andthe first and second pull-down resistance units 226 and 228 are inseries connected to each other between the output node and the groundvoltage VSSQ. A voltage applied to the output node is outputted as thefeedback pull-down resistance N_LEG_FD.

The first pull-down resistance unit 226 includes first to fifth NMOStransistors NM1, NM2, NM3, NM4 and NM5 which are in parallel connectedbetween the output node and a second node N2 and are respectively turnedon by the second fine code signal N_FN_CD<0:4>. Also, The secondpull-down resistance unit 228 includes first to fourth resistors Rn1,Rn2, Rn3 and Rn4 which are in parallel connected to the second node N2and sixth to ninth fifth NMOS transistors NM6, NM7, NM8 and NM9 whichare in series connected to each of the resistors and are respectivelyturned on by the second coarse code signal N_CR_CD<0:3>.

On the other hand, since the third and fourth pull-up resistance units222 and 224 have the same configuration as the first resistance feedbackunit 120, the detailed description of the third and fourth pull-upresistance units 222 and 224 is not illustrated. Also, the secondtermination resistance supply unit 700 includes only the first andsecond pull-down resistance units 226 and 228 which are included in thesecond resistance feedback unit described in FIG. 6. Accordingly, thesecond termination resistance supply unit 700 supplies the pull-downresistance N_LEG_RSS which is correspondent to the second coarse codesignal N_FN_CD<0:3> and the second fine code signal N_FN_CD<0:4>.

As a result, the feedback pull-down resistance N_LEG_FD supplied fromthe second resistance feedback unit 220 is created by a voltage ratio ofthe first and second pull-up code resistances to the first and secondpull-down code resistances which are correspondent to the first fine andcoarse code signals P_FN_CD<0:4> and P_CR_CD<0:3> and the second fineand coarse code signals N_FN_CD<0:4> and N_CR_CD<0:3>, respectively.

As mentioned above, as compared to the conventional semiconductor devicedescribed in FIG. 3, the second resistance feedback unit 220 furtherincludes the third pull-up resistance unit 224 and the first pull-downresistance unit 226. It is possible to finely control the feedbackpull-down resistance N_LEG_FD by further including the resistance units(the reference numerals 224 and 226) of MOS transistors.

Therefore, as shown in FIGS. 5 and 6, the rate of change in the feedbackresistance, which is controlled by the fine and coarse code signals, canhave different values. Accordingly, being different from the methodwhere resolution is improved by simply increasing the number of bits ofthe code signal with large area for it, the present invention may notincrease the chip area and the layout complexity as much.

The detailed operation of the on-die termination circuit according tothe present invention shown in FIGS. 4 to 6 will be described below.

First, if the driving signal RES is activated, the ODT control unit 800activates the control signals ODT_EN1P, ODT_EN2P and DT_UPP in thisorder. The first control unit 320 activates the second pull-up drivingsignal ODT_UPP2 in response to the control signal ODT_EN1P.

Next, the first code signal generation control unit 100 outputs a leveldifference, as the pull-up level signal P_LEG_DT, which is producedbetween the first coarse and fine code signals P_CR_CD<0:3> andP_FN_CD<0:4> and the input resistance ZQ. The first coarse code register360 which is activated by the second pull-up driving signal ODT_UPP2 andthe control signal DT_UPP controls the first coarse code signalP_CR_CD<0:3> in response to the logic level of the pull-up level signalP_LEG_DT.

The ODT control unit 800 activates the control signals ODT_EN1N,ODT_EN2N and DT_UPN in this order and the second control unit 420activates the second pull-down driving signal ODT_UPN2 in response tothe activation of the control signal ODT_EN1N.

Subsequently, the second code signal generation control unit 200 outputsa level difference, as the pull-down level signal N_LEG_DT, which isproduced between the second coarse and fine code signals N_CR_CD<0:3>and P_FN_CD<0:4> and the first coarse and fine code signals N_CR_CD<0:3>and P_FN_CD<0:4>. The second coarse code register 460 which is activatedby the second pull-down driving signal ODT_UPN2 and the control signalDT_UPN controls the second coarse code signal N_CR_CD<0:3> in responseto the logic level of the pull-down level signal N_LEG_DT.

As mentioned above, the present invention controls only the first andsecond coarse code signals P_CR_CD<0:3> and N_CR_CD<0:3> in a relativelylarge range during the initial time the driving signal is applied to it.The processing of the control in the coarse code signal repeats untilthe feedback resistance is close to the input resistance in a range ofthe resolution.

When the feedback resistance has a value similar to the inputresistance, the first and second control units 320 and 420 respectivelyactuates the first pull-up and pull-down driving signals ODT_UPP1 andODT_UPN1 in response to the transition of each of the correspondinglevel signals P_LEG_DT and N_LEG_DT. At this time, since the secondpull-up and pull-down driving signals ODT_UPP2 and ODT_UPN2 are notactivated, the first and second coarse code registers 360 and 460 areinactivated so that the current states of the first and second coarsecode signal P_CR_CD<0:3> and N_CR_CD<0:3> are stored and an update forthe coarse code signal is not made any more.

Next, since the first fine code register 340 is activated by the firstpull-up driving signal ODT_UPP1 and the control signal DT_UPP, the firstfine code signal P_FN_CD<0:4> is controlled based on the pull-up levelsignal P_LEG_DT. Similarly, the second fine code register 440 isactivated by the first pull-up driving signal ODT_UPP1 and the controlsignal DT_UPN and the second fine code signal P_FN_CD<0:4> is controlledbased on the pull-down level signal N_LEG_DT.

That is, in the present invention, after setting by the coarse codesignal, the feedback resistance is finely controlled to have aresistance value corresponding to the input resistance ZQ, bycontrolling only the first and second fine code signals P_FN_CD<0:4> andN_FN_CD<0:4>.

When the first and second coarse code signals P_CR_CD<0:3> andN_CR_CD<0:3> and the first and second fine code signals P_FN_CD<0:4> andN_FN_CD<0:4> are set, the first and second termination resistance supplyunits 500 and 700 provides the pull-up resistance and the pull-downresistance corresponding to them.

As set forth above, the present invention has two steps, in which thecoarse driving stage controls the resistance roughly and the finedriving stage controls the resistance finely, in the set of thetermination resistances N_LEG_RSS and P_LEG_RSS corresponding to theinput resistance ZQ.

In other words, in the coarse driving stage, the feedback resistancesP_LEG_FD and N_LEG_FD are roughly controlled to have a resistance valuecorresponding to the input resistance ZQ. Since a low resolution isobtained in the coarse driving stage, the coarse code signalcorresponding to the input resistance may be set quickly. In the finedriving stage, the feedback resistances P_LEG_FD and N_LEG_FD are finelycontrolled to have the same resistance value as the input resistance ZQ.

Therefore, the on-die termination circuit according to the presentinvention achieves the highly controlled termination resistance with thehigh resolution, by further including the resistance control unit inwhich the resistance is controlled by the MOS transistors provided inthe feedback unit and the termination resistance supply unit. Also, thesemiconductor device having the termination resistance according to thepresent invention can be stably driven at high frequency. In the presentinvention, the pull-up and pull-down resistances are simultaneouslyemployed; however, it is possible to design a termination circuit whichhas just one of the pull-up and pull-down resistances.

As is apparent from the above, the on-die termination circuit accordingto the present invention supports high resolution, without increasing anarea of the device, and guarantees stable operation at high frequency,by classifying the resistance control into the coarse control processingand the fine control processing.

While the present invention has been described with respect to theparticular embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. An on-die termination circuit comprising: a control unit forsequentially generating a plurality of control signals in response to adriving signal; a termination resistance supply unit for supplying atermination resistance in response to a coarse code signal having aplurality of bits and a fine code signal having a plurality of bits; anda code signal generating unit for controlling the fine code signal andthe coarse code signal in response to the plurality of the controlsignals so that the termination resistance has a level which correspondsto an input resistance, wherein the code signal generating unitincludes: a code signal generation control unit for outputting a levelsignal which corresponds to a difference between the fine and coarsecode signals and the input resistance in response to the correspondingcontrol signal; a register control unit for activating a first drivingsignal in response to a first control signal and for activating a seconddriving signal when the level signal goes from a first logic level to asecond logic level; a coarse code register for generating the coarsecode signal corresponding to the level signal in response to the firstdriving signal; and a fine code register for generating the fine codesignal corresponding to the level signal in response to the seconddriving signal.
 2. The on-die termination circuit of claim 1, whereinthe termination resistance supply unit includes a first resistance unitfor supplying a first code resistance corresponding to the coarse codesignal and a second resistance unit for supplying a second coderesistance corresponding to the fine code signal, wherein the first andsecond resistance units are in series coupled to each other in order toproduce the termination resistance.
 3. The on-die termination circuit ofclaim 2, wherein a minimum variation of the first code resistance islarger than that of the second code resistance.
 4. The on-dietermination circuit of claim 3, wherein the second resistance unitincludes first to fifth MOS transistors which are in parallel connectedto each other between a first node and an output node of the terminationresistance supply unit and receive a bit of corresponding code of thefine code signal through a gate, respectively.
 5. The on-die terminationcircuit of claim 4, wherein the first resistance unit includes aplurality of unit resistance parts which are selectively connectedbetween a power supply and the first node by a corresponding code of thecoarse code signal.
 6. The on-die termination circuit of claim 5,wherein the unit resistance part includes: a sixth MOS transistor forhaving a gate to receive the corresponding code of the coarse codesignal, being connected to the power supply; and a passive resistordisposed between the first node and the sixth MOS transistor.
 7. Theon-die termination circuit of claim 6, wherein a resistance value of thepassive resistor is larger than a turn-on resistance of the first tofifth MOS transistors.
 8. The on-die termination circuit of claim 1,wherein the code signal generation control unit includes: a resistancefeedback unit for receiving the input resistance and the fine and coarsecode signals and for outputting a feedback resistance; a level detectingunit for outputting a detecting signal in response to the first controlsignal by detecting a level of the feedback resistance based on areference resistance; and an amplifier for amplifying the detectingsignal in response to a second control signal and for outputting theamplified signal as the level signal.
 9. The on-die termination circuitof claim 8, wherein the resistance feedback unit includes: a firstfeedback resistance unit for supplying a first resistance correspondingto the coarse code signal; and a second feedback resistance unit forsupplying a second resistance corresponding to the fine code signal,being connected to the first feedback resistance unit in series.
 10. Theon-die termination circuit of claim 9, wherein the second feedbackresistance unit includes seventh to eleventh MOS transistors, each ofwhich receive the fine code signal through a gate, in parallel disposedbetween a second node and an output node of the resistance feedbackunit.
 11. The on-die termination circuit of claim 10, wherein the firstfeedback resistance unit includes a plurality of unit feedbackresistance parts which respectively connect the power supply to thesecond node in response to a corresponding code of the coarse codesignal.
 12. The on-die termination circuit of claim 11, wherein the unitfeedback resistance part includes: a twelfth MOS transistor for having agate to receive the corresponding code of the coarse code signal, beingconnected to the power supply; and a passive resistor connected betweenthe twelfth MOS transistor and the second node.
 13. The on-dietermination circuit of claim 1, wherein the coarse code registergenerates the coarse code signal of plurality of bits based on a logiclevel of the level signal when a third control signal and the seconddriving signal are activated.
 14. The on-die termination circuit ofclaim 13, wherein the fine code register generates the fine code signalof plurality of bits based on a logic level of the level signal when athird control signal and the second driving signal are activated.
 15. Anon-die termination circuit comprising: a driving control means forsequentially generating a plurality of control signals in response to adriving signal; a first termination resistance supply means forsupplying a termination pull-up resistance in response to a first coarsecode signal having a plurality of bits and a first fine code signalhaving a plurality of bits; a first code signal generating means forcontrolling the first coarse and fine code signals in response to theplurality of the control signals so that the termination pull-upresistance has a level which corresponds to an input resistance; asecond termination resistance supply means for supplying a terminationpull-down resistance in response to a second coarse code signal having aplurality of bits and a second fine code signal having a plurality ofbits; and a second code signal generating means for controlling thesecond coarse and fine code signals in response to the plurality ofcontrol signals so that the termination pull-down resistance has a levelwhich corresponds to the termination pull-up resistance, wherein thesecond code signal generating means includes: a first resistancefeedback unit for receiving the first and second fine code signals andthe first and second coarse code signals and for outputting a feedbackpull-down resistance; a first coarse code generating unit for producingthe second coarse code signal in order that the feedback pull-downresistance has a level corresponding to a reference resistance; and afirst fine code generating unit for producing the second fine codesignal in order that the feedback pull-down resistance has a levelcorresponding to the reference resistance while the first coarse codesignal generating unit is inactivated.
 16. The on-die terminationcircuit of claim 15, wherein the first resistance feedback unitincludes: a first resistance unit for supplying a first feedbackresistance corresponding to the first coarse code signal; a secondresistance unit for supplying a second feedback resistance correspondingto the first fine code signal; a third resistance unit for a thirdfeedback resistance corresponding to the second coarse code signal; anda fourth resistance unit for supplying a fourth feedback resistancecorresponding to the second fine code signal, wherein the firstresistance feedback unit supplies the feedback pull-down resistance byconnecting in series the first and second resistance units between afirst supply voltage and an output node and the third and fourthresistance units between a second supply voltage and the output node.17. The on-die termination circuit of claim 16, wherein a minimumvariation of the first and third feedback resistance is larger than thatof the second and fourth feedback resistance.
 18. The on-die terminationcircuit of claim 17, wherein the second and fourth resistance unitincludes first to fifth MOS transistors each of which has a gate toreceive an input signal and are in parallel connected to each other. 19.The on-die termination circuit of claim 18, wherein the first and thirdresistance unit includes: sixth to ninth MOS transistors each of whichreceives an input signal through a gate, being connected to each other;and first to fourth passive resistors which are connected to sixth toninth MOS transistors, respectively.
 20. The on-die termination circuitof claim 19, wherein the first coarse code generating unit includes: alevel detecting unit for outputting a pull-down detecting signal bydetecting a level of the feedback pull-down resistance based on thereference resistance in response to a first control signal; an amplifierfor amplifying the pull-down detecting signal in response to a secondcontrol signal and for outputting the amplified signal as a pull-downlevel signal; a first register control unit for activating a firstpull-down driving signal in response to the first control signal and forproducing a second pull-down driving signal when the pull-down levelsignal goes from a first logic level to a second logic level; and afirst coarse register for generating the second coarse code signal basedon a logic level of the pull-down level signal in response to a thirdcontrol signal and the first pull-down driving signal.
 21. The on-dietermination circuit of claim 20, wherein the fine code generating unitincludes a first fine register for generating the second fine codesignal based on a logic level of the pull-down level signal and inresponse to the third control signal and the first pull-down drivingsignal.
 22. The on-die termination circuit of claim 21, wherein thefirst code signal generating means includes: a second resistancefeedback unit for receiving the first fine and coarse code signals basedon the input resistance and for outputting a feedback pull-upresistance; a second coarse code generating unit for producing the firstcoarse code signal in order that the feedback pull-up resistance has alevel corresponding to the reference resistance; and a second fine codegenerating unit for producing the first fine code signal in order thatthe feedback pull-up resistance has a level corresponding to thereference resistance while the second coarse code signal generating unitis inactivated.
 23. The on-die termination circuit of claim 22, whereinthe second resistance feedback unit includes: a first pull-up feedbackresistance unit for supplying a first code resistance corresponding tothe first coarse code signal; and a second pull-up feedback resistanceunit for supplying a second code resistance corresponding to the firstfine code signal, wherein the second resistance feedback unit suppliesthe feedback pull-up resistance by connecting in series the first andsecond pull-up feedback resistance units.
 24. The on-die terminationcircuit of claim 23, wherein a minimum variation of the first coderesistance is larger than that of the second code resistance.
 25. Anon-die termination circuit comprising: a termination resistance supplyunit for supplying a termination resistance in response to a coarse codesignal having a plurality of bits and a fine code signal having aplurality of bits; a resistance feedback unit for receiving the finecode signals and the coarse code signals and for outputting a feedbackpull-down resistance; a coarse code generating unit for producing thecoarse code signal in order that the feedback pull-down resistance has alevel corresponding to a reference resistance; and a fine codegenerating unit for producing the fine code signal in order that thefeedback pull-down resistance has a level corresponding to the referenceresistance while the coarse code signal generating unit is inactivated,wherein the resistance feedback unit includes: a first feedbackresistance unit for supplying a first resistance corresponding to thecoarse code signal; and a second feedback resistance unit for supplyinga second resistance corresponding to the fine code signal, beingconnected to the first feedback resistance unit in series.
 26. A methodfor driving an on-die termination circuit comprising: generating aplurality of control signals in response to a driving signal; supplyinga termination resistance in response to a coarse code signal having aplurality of bits and a fine code signal having a plurality of bits; andcontrolling the fine code signal and the coarse code signal in responseto the plurality of the control signals so that the terminationresistance has a level which corresponds to an input resistance, whereingenerating a plurality of control signals includes: outputting a levelsignal which corresponds to a difference between the fine and coarsecode signals and the input resistance in response to the correspondingcontrol signal; activating a first driving signal in response to a firstcontrol signal and for activating a second driving signal when the levelsignal goes from a first logic level to a second logic level; generatingthe coarse code signal corresponding to the level signal in response tothe first driving signal; and generating the fine code signalcorresponding to the level signal in response to the second drivingsignal.
 27. The method of claim 26, wherein a minimum variation of thetermination resistance which is controlled by the fine code signal issmaller than that of the termination resistance which is controlled bythe coarse code signal.